Certain thermoplastic resins, e.g. polyalkylene terephthalates, polyamide and polycarbonate, and their blends are well known and widely used because of their excellent mechanical properties. A significant disadvantage characterizing these materials is a susceptibility to deterioration upon exposure to hot water or water vapor.
Incorporation of carbodiimides in polyalkylene terephthalate is known to improve the resistance of this resin to hydrolysis. U.S. Pat. No. 4,110,302 disclosed a process for producing a reinforced polyalkylene terephthalate molding resin composition. In the process polyalkylene terephthalate polymer in the molten state is mixed with a reinforcing agent and polycarbodiimide. The polycarbodiimide is derived from an aromatic diisocyanate and contains at least two carbodiimide units per polycarbodiimide molecule.
U.S. Pat. No. 4,071,503 disclosed a process for preparing a polycarbodiimide modified thermoplastic polyester whereby polycarbodiimide is incorporated into the structure of thermoplastic saturated polyester, having at least one carboxyl end group. The polycarbodiimide is derived from an aromatic diisocyanate and contains at least three carbodiimide units per polycarbodiimide molecule.
U.S. Pat. No. 5,733,959 disclosed a thermoplastic molding composition comprising polyester or its blends with polycarbonate or a polyamide and a carbodiimide conforming to a structural formula, the composition said to feature improved resistance to hydrolysis.
U.S. Pat. No. 6,855,758 disclosed a hydrolysis stabilizer in the context of polyester. In one preferred embodiment, the stabilizer is polymeric aromatic-carbodiimides and a blend of an organic phosphite and hydroxyphenyl propionate.
Also presently relevant is the article “Sterically Hindered Carbodiimides: Use of Selective Agents for Hydrolytic Protection of Ester and Imide Groups-Review of Past, Present, and Future” McAfee, E. R. Rhein Chemie Corporation, Pittsburgh, Pa., USA. Proceedings of the SPI Annual Technical/Marketing Conference (1992), 34th (Polyurethanes 92), pp 122-7.
Thermoplastic molding compositions that contain polyester carbonate and an inorganic powder, such as boehmite have been disclosed in U.S. Pat. No. 6,831,120.